In many prior art processes for preparing diketones, the diketones are minor by-products or the diketones are prepared by commercially impractical circuitous routes. Some diketones are reported to be prepared by well-known Friedel-Crafts reactions using diacid chlorides and such catalysts as AlCl.sub.3. An example is contained in U.S. Pat. No. 4,816,556 which describes preparation of two diketones by reaction of 2 moles of diphenyl ether with 2 moles terephthalyl chloride (or 2 moles isophthalyl chloride) with 4 moles aluminum chloride as catalyst. Some disadvantages of this process are high cost which results from (1) the use of expensive diacid chlorides instead of diacids and (2) the use of large amounts of catalyst which is destroyed in the workup. Disposal of large amounts of aluminum wastes and corrosion from HCl by-product could also present problems Another prior art process discloses preparation of a diketone from isophthalic acid and anisole. This process is disclosed by Mitsuru Ueda and Masaki Sato, Makromol. 20, pp. 2675-2678 (1987). This diketone is not the type of this invention since it cannot be polymerized to give a polyketone. The reaction medium was PPMA, which is a mixture of phosphorus pentoxide and methanesulfonic acid, at a particular weight ratio. The phosphorus pentoxide acts as a dehydrator in that it takes up the water that is a product of the reaction and is itself converted to phosphorus acids. There are disadvantages to the use of phosphorus pentoxide in this reaction:
1. Handling. Ueda and Kano state that the phosphorus pentoxide "is difficult to handle because of its high reactivity toward moisture."
2. Recovery of dehydrator. The phosphorus acids are not practically recoverable for recycling. They are generally disposed of in an aqueous workup.
3. Cost. The inability to recycle phosphorus pentoxide makes a PPMA process more expensive than that of the present invention.
None of the above-described prior art discloses preparation of a keto-acid.
It would be highly desirable to have a process for preparing diketones and keto-acids that overcomes the problems of prior art processes.